SERS substrates

ABSTRACT

A surface-enhanced Raman spectroscopy substrate device, including a base substrate, a single or multiple layered nanostructure that contains metals, and a plasma coating. The nanostructure metal is selected from the group including silver, gold, platinum, copper, titanium, chromium, and combinations thereof. The plasma coating has a thickness of 1-200 nm and may locate on the nanostructure layer or on the base substrate. The plasma coating can precisely control the surface characteristics, including surface energy, hydrophilicity, and contact angle, of the SERS device and may then help to regulate the SERS substrate with well defined and uniform water/oil contact angle with small standard deviation. The water contact angle of the SERS substrate may range from 20 to 140 degrees.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent applicationSer. No. 13/106,965, filed on May 13, 2011.

TECHNICAL FIELD

The present invention relates generally to materials science, surfaceengineering, spectroscopy, and, more particularly, surface enhancedRaman spectroscopy (SERS).

BACKGROUND

Optical-based sensing has several major advantages over electronicsensing because optical sensing reveals spectral fingerprints ofchemical compounds rapidly and accurately, thus significantlysimplifying the detection process and reducing false alarms. One of themost promising optical sensing techniques is surface enhanced Ramanspectroscopy (SERS), which employs noble metal nanostructures todramatically enhance Raman signals. With the aid of metallicnanostructures, such as gold- or silver-based nanosubstrates, a Ramansignal can be enhanced by 10⁴ to 10⁸ times or even higher. Thisenhancement is due to the generation of spatially localized surfacePlasmon resonance (SPR) “hot spots” where huge local enhancements ofelectromagnetic field are obtained. The location of “hot spots” on themetallic structures depends on the geometry of the nanostructures, theexcitation wavelength, and polarization of the optical fields. SERS canpotentially reach the limit of detection down to the lowparts-per-billion (ppb) and theoretically to the single molecule level.Thus, SERS has been increasingly used as a signal transduction mechanismin biological and chemical sensing.

One of the most critical components for surface enhanced Ramanspectroscopy (SERS) is the development of suitable substrates that canactivate surface plasmon resonance (SPR). In principle, sharp edges ofthe metal surface topography can produce SPR as induced by an incidentexcitation laser, thus generating an enormously enhanced electromagneticfield of signals that occur within highly localized optical fieldsaround the metallic structures. When designing a surface structuresuitable for SERS application, the size of the metal islands, grains, orparticles constructed onto the supporting substrate varies from severalnanometers to microns. Generally, a nanoscale structure has multipleadvantages over a microscale one because the plasmon localizationbecomes more intensified at a nanoscale due to a strong spatialconfinement effect. As the size of bodies decrease, theirsurface-to-volume aspect ratios increase. A high surface-to-volume ratiogives rise to an increased number of probe molecules available forcapture in the vicinity of metal surface within a distance on the orderof nanometers.

Current efforts for nanostructure development can be categorized aseither direct or indirect methods. Direct methods involve manipulatingthe metal directly to prepare a metal substrate with preferred micro- ornanostructures, while indirect methods employ other materials, such asceramics, to prepare the preferred micro- or nanostructures first andthen incorporate the metal onto these structures.

However, there are technical and non-technical challenges in fabricationof SERS substrates that significantly impede the commercial applicationsof SERS. For example, most existing SERS substrates exhibit inconsistentactivities and it is a common problem that a subtle change in thesubstrate manufacturing process can produce significant changes of theRaman signal. Such inconsistencies make quantitative or evensemi-quantitative analysis difficult.

Therefore, there is a need for better SERS substrates withwell-controlled surface characteristics to achieve measurement accuracyand consistency in SERS analysis. There is also a need to provide newand improved fabrication method for manufacturing SERS substrates withwell-controlled surface characteristics. There is yet another need todevelop new and improved SERS analysis protocols for variousapplications, such as food safety, water safety, homeland security andother areas. The present novel technology addresses these needs.

DESCRIPTION OF DRAWINGS

FIG. 1A is a side elevation view of a SERS substrate having a plasmadeposition layer between a base substrate and an incomplete metallicnanostructure layer made of SERS active metals, according to oneembodiment of the invention.

FIG. 1B is a side elevation view of a SERS substrate with a metalliccoating layer deposited upon a layer of nanostructures, with additionalplasma coating deposited upon the metallic coating layer, according to asecond embodiment of the invention.

FIG. 1C is a side elevation view a SERS substrate with multiple layersof material thereon, including a first metallic coating layer, ananostructure layer, a second metallic layer, and a plasma coatinglayer, according to a third embodiment of the present invention.

FIG. 2A is an SEM image of an exemplary nanostructure layer of anincomplete monolayer of nanoparticles.

FIG. 2B is an SEM image of an exemplary nanostructure layer of acomplete monolayer of nanoparticles.

FIG. 2C is an SEM image of an exemplary nanostructure layer of adouble-layer of nanoparticles.

FIG. 3 is an SEM image of an exemplary nanostructure layer coated with ametallic coating layer. The metallic coating layer itself is composed ofmetallic nanoparticles.

FIG. 4 is an SEM image of an exemplary SERS substrate with a layer ofnanostructures, a metallic coating layer on the nanostructures, and aplasma coating on the metallic coating.

FIG. 5 graphically illustrates the oxygen flow rate dependence of thewater surface contact angles of plasma nanocoatings, which may beapplied to FIGS. 1A-1C, as obtained from a mixture of trimethylsilane(TMS) and oxygen with different gas ratios.

FIG. 6A graphically illustrates a first droplet on a substrate having afirst contact angle and a first concentration of residue.

FIG. 6B graphically illustrates a second droplet on a substrate having asecond contact angle and a second concentration of residue.

FIG. 6C graphically illustrates a third droplet on a substrate having athird contact angle and a third concentration of residue.

FIG. 7 is an SEM image of SERS substrates with a layer of Ag nanocubeson top of Au thin film composed of smaller Au nanoparticles.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention and presenting its currently understood best mode ofoperation, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, with such alterations and furthermodifications in the illustrated device and such further applications ofthe principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The novel technology relates to an improved SERS substrate withwell-controlled surface chemistry and surface features, structures,properties, and the like, which give rise to consistent and reliableSERS detection. Specifically, the novel technology relates to thephysical and chemical manipulation of the SERS substrate surface toyield control of surface chemical adsorption of analyte molecules,droplet size and solvent evaporation processes. Particularly, ananoscale thin coating with predetermined surface characteristics, suchas surface tension, is applied onto a SERS surface, such as through lowtemperature plasma deposition techniques. The surface characteristics,such as surface tension, of the nanocoating are adjustable andcontrollable by manipulating the plasma chemistry or plasma gascomposition for the plasma deposition. Particularly, the contact anglewith any particular analyte or analyte solution may be preciselycontrolled over a large range with small special variation (standarddeviation). Through the controlled application of such plasmananocoating, the sampling volume and area on SERS substrates may be keptconsistent from spot to spot and/or from substrate to substrate. As aresult, consistent chemical absorption of analyte molecules on SERSsubstrates may be achieved, and reliable and reproducible Raman signalsmay be detected.

Particularly, the present SERS substrate includes a SERS-active surfacethat contains nanostructures with SERS-active metals and a plasmacoating at least partially deposited upon or beneath the SERS surfaces.The SERS surface may be achieved by direct or indirect methods. Theinstant novel substrate may feature zero-dimensional, one-dimensional,or two-dimensional surface nanostructures. The novel substrate mayinclude any roughened surfaces, nanoparticles, nanoaggregates,nanopores/nanodisks, nanorods, nanowires, and/or a combination thereof,as well as microstructures, such as a silver-coated microarray and/or agold-coated microarray. The novel substrates may include multiplelayered micro and nano-structures made of SERS active metals. Theinteraction within and between layers of micro and nanostructures maycreate more hot spots for SERS enhancement.

According to one embodiment of the present novel technology, the SERSsurface may include a base substrate and a metallic nanostructure layerdeposited upon the base substrate. As shown in FIG. 1A, the novel SERSsubstrate 10 may include a base substrate 12 and a metal nanostructurelayer 14′ as well as a plasma coating layer 20 deposited at leastpartially upon the base substrate 12. The nanostructure layer 14′ isdeposited upon the plasma layer 20. The nanomaterial employed in thenanostructure layer 14′ may be any SERS-active metallic material, suchas silver, gold, copper, platinum, titanium, chromium, combinationsthereof or the like. In addition, the nanostructure layer 14′ may assumeany form, such as nanoparticles, nanoaggregates, nanopores/nanodisks,nanorods, nanowires, or combinations thereof. The substrate 12 may beany ceramic, polymer, or metal materials that are flat and may alsoprovide sufficient mechanical support, such as silicon, quartz(crystalline silica), glass, zinc oxide, alumina, Paraffin film,polycarbonate (PC), combinations thereof and the like. Typically, thesubstrate 12 materials are generally inert and do not react with analyteand interfere with SERS detection. More typically, the substrate 12materials have simple Raman spectra with few peaks. The plasma coatinglayer 20 is typically deposited from low-temperature gas plasmas withthickness in nanoscale (a few to a few hundred nanometers). The surfacechemistry and surface energy of the plasma coating layer 20 may becontrolled and adjusted by plasma gas selection. The plasma gases fordepositing plasma coating layer 20 are typically gases or vapors ofsilicon-carbons, hydrocarbons, fluorocarbons, mixtures thereof, andtheir mixtures with simple gases such as oxygen, nitrogen, air, nitrousoxide, ammonia, carbon dioxide, water vapor, argon, helium, mixturesthereof, and the like. The plasma may be produced at a reduced pressureor at one atmospheric pressure by various plasma sources of, but notlimited to, direct current, alternating current, audio-frequency,radio-frequency power sources with both a continuous wave and pulsedwave.

According to another embodiment of the present novel technology, a novelSERS substrate 10 may include a base substrate 12, a nanostructure layer14, a metallic coating 16, and a plasma coating layer 20. FIG. 1B is anillustration of one exemplary setup of the embodiment. As shown in FIG.1B, the SERS substrate 10 is formed on a base substrate 12 with ananostructure layer 14 and a metallic coating layer 16 whereas thenanostructure layer 14 is deposited upon the base substrate 12 and themetallic coating layer 16 is deposited upon the nanostructure layer 14.A plasma layer 20 is deposited upon the metallic coating layer 16. Thenanostructure layer 14 may assume any form, such as nanoparticles,nanoaggregates, nanopores/nanodisks, nanorods, nanowires, orcombinations thereof. The materials employed in the nanostructure layer14 may be any ceramic, polymer, and metal materials. The metalliccoating layer 16 may be a thin film with uniform thickness, be a thinfilm of certain nanoroughness, or be composed of smaller nanostructures,such as nanoparticles. The materials of employed in the metallic layer16 may be any SERS-active metallic material, such as silver, gold,copper, platinum, titanium, chromium, combinations thereof or the like.The substrate 12 may be any of the ceramic, polymer, or metal materialsas described above regarding FIG. 1A, and the plasma coating layer 20may be any of the materials described above regarding FIG. 1A.

According to another embodiment, a novel SERS substrate 10 may include abase substrate 12, a first metallic coating layer 16′, a nanostructurelayer 14, a second metallic coating layer 16″, and a plasma coatinglayer 20. As shown in FIG. 1C, the SERS surface 10 includes a basesubstrate 12, a first metallic layer 16′, a nanostructure layer 14, asecond metallic layer 16″, and a plasma coating layer, where the firstmetallic layer 16′ is deposited upon the base substrate 12, thenanostructure layer 14 is deposited upon the first metallic layer 16′, asecond metallic layer 16″ is deposited on the nanostructure layer 14,and the last plasma coating layer 20 is then applied. A plasma coatinglayer 20 is deposited at least partially upon the second metallic layer16″. The first metallic layer 16′ and the second metallic layer 16″ maybe of same or different SERS-active metals materials. The metalliccoating layer 16′ and 16″ may be a thin film with uniform thickness, bea thin film of certain nanoroughness, or be composed of smallernanostructures, such as nanoparticles. The materials of employed in themetallic layer 16′ and 16″ may be any SERS-active metallic material,such as silver, gold, copper, platinum, titanium, chromium, combinationsthereof or the like. The substrate 12 may be any of the ceramic,polymer, or metal materials as described above regarding FIGS. 1A and 1BThe plasma coating layer 20 may be any of the materials described aboveregarding FIGS. 1A and 1B.

FIG. 1A-C illustrate configuration options for multi-layered structures10, where a plasma coating 20 may be used to either provide full orincomplete substrate coverage. Further, the plasma coating 20 may resideon the top, the bottom, or between other layers 14, 16. Thenanostructures 14 may likewise either fully or incompletely cover thesubstrate 12. In addition to the enhanced SERS sensitivity arising fromthe plasma coating 20, control of the surface chemistry, the presence ofmultiple layers of nanostructures 14 (such as Au nanoparticles 14positioned over an Au thin film or layer formed from smaller Aunanoparticles), and the like also may combine to improve the SERSenhancement factors.

The nanostructure layer 14 in FIG. 1B and FIG. 1C may be formed from anynanomaterials, such as nanoparticles, nanoaggregates,nanopores/nanodisks, nanorods, nanowires, or combinations thereof. Thematerials employed in the nanostructure layer 14 may be any ceramic,polymer, and metal materials. For example when the nanostructure layer14 employs non-metallic nanoparticles, the nanostructure layer 14 may bedeposited as an incomplete monolayer, a complete monolayer, adouble-layer, or a plurality of layers, of nanoparticles, as illustratedin FIGS. 2A through 2C. FIGS. 2A-2C are SEM images of various depositionpatterns of SiO₂ nanoparticles as deposited on the base substrate 12(defining the nanostructure layer 14 for a respective particularembodiment). FIG. 2A is an SEM image of an incomplete monolayer of SiO₂nanoparticles 14, FIG. 2B is an SEM image of monolayer SiO₂nanoparticles 14, and FIG. 2C is an SEM image of a double-layer of SiO₂nanoparticles 14.

The metallic coating layer 16 may be a thin film with uniform thickness,be a thin film of certain nanoroughness, or be composed of smallernanostructures, such as nanoparticles. The materials of employed in themetallic layer 16 may be any SERS-active metallic material, such assilver, gold, copper, platinum, titanium, chromium, combinations thereofor the like. FIG. 3 is an SEM image of an SiO₂ nanostructure layer 14coated with sputtered Au coating 16. In this particular case, the Aucoating layer 16 is composed of Au nanoparticles, which also contributeto SERS enhancement beyond the nanostructures provided by SiO₂ layer 14.

The plasma coating layer 20 is typically found in the present SERSsubstrate 10 and aids in producing the desired surface characteristics.FIG. 4 is an SEM image of an exemplary SERS substrate 10, wherein theSiO₂ nanoparticle layer 14 is firstly deposited upon Si wafer 12 andthen coated with Au coating layer 16 followed by the plasma coatinglayer 20. The plasma coating layer 20 may be deposited using anyconvenient deposition method, such as chemical deposition. For example,according to one embodiment, low-temperature gas plasmas are partiallyionized gases that are mainly produced at a reduced pressure and containhighly reactive particles including electronically excited atoms,molecules, ionic and free radical species. Depending on the plasmachemistry or gas composition, these highly reactive plasma species canclean and etch surface materials and/or bond to various substrates toform a nanoscale thin layer of plasma coating 20. Such plasma coatings20 can be controlled in terms of coating thickness and surfacecharacteristics such as surface chemistry, surface energy, and surfacehydrophilicity by adjusting plasma conditions and/or plasma chemistry.The plasma coating thickness 20 is typically in the range of from about1 nm to about 200 nm, with a more typical thickness range of betweenabout 1 nm and about 50 nm.

The surface energy or surface hydrophilicity of the plasma coatings 20may be expressed by water contact angle and controllably adjusted byplasma chemistry or plasma gas composition. A smaller water contactangle corresponds to a more hydrophilic (or less hydrophobic) surface,while a larger water contact angle indicates a less hydrophilic (or morehydrophobic) surface. For example, as shown in FIG. 5, the water contactangle of the plasma coatings 20 obtained from a mixture oftrimethylsilane and oxygen can be controllably adjusted from about 100degrees to below about 40 degrees.

FIG. 6 illustrates the influence of the water contact angle on theaqueous droplet size and droplet residue size. Generally speaking, thecase in FIG. 6A is not preferred as the aqueous solution spread in theSERS substrate and the size of the droplet may not be reliablycontrollable and the concentration of the residue is likewise difficultto predict. Such uncontrollability and unpredictability of the surfaceproperties of the substrate 10 make SERS quantitative analysis or evento semi-quantitative analysis difficult. As shown in FIGS. 6B and 6C,with droplets having substantially the same volume, droplet residueshave different sizes and concentrations. Considering a certain SERSsubstrate can only provide quantitative measurement for a certainchemical, such as 10 PPB-10 PPM or 1 PPM-500 PPM, it is important tocontrol the analyte concentration in the residue. Depending on theconcentration of the analyte solution, optimal conditions of surfacechemistry, surface energy, water contact angle and/or hydrophilicity maybe selected. For example, in order improve the limit of the detection ofan analyte in aqueous solution, more hydrophobic surface with high watercontact angle, leading to high concentration of the droplet residue,should be used. As another example, in order improve the limit ofdetection of analyte in oil solution, more hydrophilic surface with lowwater contact angle, which lead to high contact angle for oil and highresidue concentration, may be selected. In addition, it is advantageousto keep the surface energy or water contact angle substantially uniformacross a SERS substrate surface and between different SERS substratesfrom different batches, as the same contact angle or smaller standarddeviation will lead to the same or similar residue concentration forquantitative analysis. Thus, the plasma coating layer 20 provides ameans for predetermining surface characteristics selected from the groupincluding surface energy, hydrophilicity, and contact angle with analytesolution so as to control, vary and optimize the SERS substrate 10 for agiven energy source (laser type), a given analyte, and given solvent,and the like.

The water contact angles of the plasma coatings 20 are typically in therange of between about 0 degrees (very hydrophilic) to about 170 degrees(superhydrophobic), and more typically between about 80 degrees andabout 140 degrees for measuring trace amount analyte in aqueous solutionand about 20 degrees to about 60 degrees for trace amount analyte inorganic solution. For the surface with 20-60 degree water contact angle,it is expected the contact angle for an organic solution will be over 90degree. The typical contact angles may decrease from values over 80degrees to values below 80 degrees for detection of aqueous samples withrelatively high concentration and the typical contact angles mayincrease from values less than 60 degrees to values greater than 90degrees for detection of organic samples with relatively highconcentration. The controlled surface energy or hydrophilicity of theplasma coatings 20 can well confine the liquid aqueous sample area for apreselected sample volume and thus achieve consistent Raman signals fora same sample concentration. By controlling the surface energy orsurface hydrophilicity of the SERS substrates, the contact area of apreselected sample volume on the substrate surface may also becontrolled when organic solvents are used to prepare the samplesolution, such as oil based solution, was applied. The water contactangles and detection limits between the substrate without plasma coatingand the substrate with plasma coating may be compared as shown inTable 1. The results of the comparison indicate that plasma coated SERSsubstrate 10 had higher water contact angles, better confined the samplecontact areas on the substrates, and consequently yielded improveddetection limits. Moreover, the standard deviation of the contact anglealso decreased after the plasma coating, which is also very beneficialfor quantitative or semi-quantitative analysis, as the actual testedareas have a more constant amount of residue after evaporation. Thesamples with plasma coating 20 shows very consistent results on 6 inchwafers, while the samples without plasma coating show much largervariation in different locations on a 6 inch wafer.

TABLE 1 Water surface contact angles and detection limits of theAu-coated SERS substrates with and without plasma coating DetectionLimits for Water Contact Angle melamine in aqueous Au Coated Substrates(standard deviation) solution Without plasma 79° ± 12° 250 ppb (notconsistent coating result) With plasma coating 109° ± 4°  100 ppb(consistent 100 ppb result) (consistent result)

Example 1

An aqueous colloidal suspension of SiO₂ nanoparticles (20-100 nm) ofconcentration between about 0.5%-5% may be prepared by adding apredetermined quantity of SiO₂ to water or by diluting high a highlyconcentrated colloidal suspension of SiO₂ with water. Magnetic stirringcan be used to achieve better dispersion of the silica nanoparticles.Droplets of SiO₂ nanoparticle colloidal suspension may be used to coat aSi wafer, such as by using a spin coater. FIGS. 2A-2C show formation ofan incomplete silica nanoparticle monolayer, a complete SiO₂nanoparticle monolayer, and a double-layer SiO₂ nanoparticle coating,respectively, on Si wafers. After the coating process, a gold coatingcontaining gold nanoparticles (10-20 nm) may be applied on the SiO₂nanoparticle coatings. FIG. 3 shows a typical SEM image of an Aunanoparticle-coated SiO₂ nanoparticle coating. The Au coating thicknesstypically may range from 10 nm to 50 nm. After the deposition of Aucoating, the substrate becomes SERS-active. Next, a plasma coating oftypical thickness of 2-50 nm is then applied over the SERS-activenanosubstrates. FIG. 4 shows a typical SEM image of a plasma coatedSERS-active nanosubstrate. The SiO₂ nanoparticles size, Au coatingthickness, and the type and thickness of plasma coating may all betailored to optimize performance for certain wavelength of laser. Theplasma coating 20 may not have a uniform thickness and may not yieldfull coverage of the Au metal nanoparticles.

A typical application of the novel SERS substrate is for food safetyapplications. Recent food safety incidents involving milk and infantformula contaminated with toxic melamine have raised a great deal ofconcerns of consumers. Traditional analytical methods such as HPLC aretime-consuming and labor-intensive, while using SERS coupled with thenovel SERS substrates, melamine in foods can be detected quickly andaccurately. The detection limit could reach the parts per billion (PPB)level. The SERS measurement time is typically short, typically within 15minutes, which is much faster than traditional methods.

Example 2

FIG. 7 shows one example of multiple layered SERS active nanostructures14. The first layer Au coating 16′ was sputtered onto a glass substrateand a second layer Ag nanocubes 14′ was dip-coated onto the Au coatedglass substrate 12. Coverage of the second Ag nanocube coating 14′ iscontrollable by concentration and/or other techniques, and the Agnanocubes 14′ may also be applied via a spin coating technique. It isexpected that the Au nanoparticles 16′ and Ag nanocubes 14′ may workbest with different laser wave lengths and may be sensitive to differentchemicals. Such a combination coating may allow for the fabrication ofSERS substrates 10 tailored for unique and enhanced performance andsensitivity as compared to traditional SERS substrates or evensubstrates 10 having uniform nanostructure layers of the same metal ormetal alloy. In addition, the different nanostructures 16′, 14′ mayinteract with each other to improve the enhancement factors, such as bycreating hot-spots between different layers 14′, 16′ of nanostructures.For example, if the top and bottom layers 14′, 16′ have nanostructuresof significantly different sizes and/or define a significant size gap(typically over 10 nm or over 30% of the smaller one), the two layers14′, 16′ may interact to substantially increase SERS sensitivity andalso work for different laser wave lengths.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character. It is understood that theembodiments have been shown and described in the foregoing specificationin satisfaction of the best mode and enablement requirements. It isunderstood that one of ordinary skill in the art could readily make anigh-infinite number of insubstantial changes and modifications to theabove-described embodiments and that it would be impractical to attemptto describe all such embodiment variations in the present specification.Accordingly, it is understood that all changes and modifications thatcome within the spirit of the invention are desired to be protected.

What is claimed is:
 1. A device for facilitating SERS analysis,comprising: a first substrate; a plurality of nanostructures disposed onthe first substrate to define a nanocoated surface; and a plasmadeposition layer disposed on the first substrate at least partiallycontacting the nanocoated surface; wherein the nanocoated surface is atleast partially coated with a second metallic layer.
 2. A surfaceenhanced Raman spectroscopy device, comprising: a base substrate; ananostructure layer at least partially covering the base substrate; ametallic nanostructure coating layer deposited at least partially overthe nanostructure layer; and a plasma deposition layer deposited atleast partially over all the nanostructures on the first substrate.
 3. Adevice for SERS (surface-enhanced Raman spectroscopy) analysis,comprising: a SERS-active surface defining an array of SERS-active metalnanostructures, wherein the nanostructures are selected from the groupincluding roughened surfaces, nanoparticles, nanoaggregates,nanopores/nanodisks, nanorods, nanowires, conductive metal coatedmicroarrays, and combinations thereof; and a plasma coating layer atleast partially deposited upon the SERS-active surface; wherein themetal nanostructures are disposed between the plasma coating layer and asubstrate.
 4. A device for SERS (surface-enhanced Raman spectroscopy)analysis, comprising: a SERS-active surface defining an array ofSERS-active metal nanostructures, wherein the nanostructures areselected from the group including roughened surfaces, nanoparticles,nanoaggregates, nanopores/nanodisks, nanorods, nanowires, conductivemetal coated microarrays, and combinations thereof; and a plasma coatinglayer at least partially deposited upon the SERS-active surface; whereinthe metal nanostructures are disposed between the plasma coating layerand a substrate; and wherein the plasma coating layer partially coversthe metal nanostructures.
 5. A device for SERS (surface-enhanced Ramanspectroscopy) analysis, comprising: a SERS-active surface defining anarray of SERS-active metal nanostructures, wherein the nanostructuresare selected from the group including roughened surfaces, nanoparticles,nanoaggregates, nanopores/nanodisks, nanorods, nanowires, conductivemetal coated microarrays, and combinations thereof; and a plasma coatinglayer at least partially deposited upon the SERS-active surface; whereinthe plasma coating is positioned between multiple layers of SERS-activestructures to serve as spacer defining distances therebetween.
 6. A SERSdevice, comprising: a base substrate; a plurality nanomaterial layersoperationally connected to the base substrate, each respective layerdefining a plurality of metallic nanoparticles; a plurality of plasmacoating layers operational connected to the base substrate; whereinrespective nanomaterial layers alternate with respective plasma coatinglayers.